Regulation of osteoclastogenesis and arthritic bone resorption by RBP-J Osteoclasts play an important role not only in physiological bone development and remodeling, but also function actively as key pathogenic cells leading to musculoskeletal tissue damage and accelerating pathogenesis of diseases characterized by inflammatory osteolysis, including rheumatoid arthritis (RA), psoriatic arthritis, periodontitis and peri-prosthetic loosening. In contrast to the extensive study of the positive regulation of osteoclastogenesis, the feedback inhibitory mechanisms that negatively regulate the magnitude of osteoclastogenesis and bone resorption, especially in pathological conditions, are little appreciated. Our long term goals are to identify and understand the inhibitory mechanisms and to utilize this knowledge in development of new therapeutic approaches to diseases associated with inflammatory osteolysis. Using miRNA-seq, we have obtained the genome-wide profile of miRNA expression induced by TNF-??in osteoclast precursors. We furthermore identified miR-182 as a novel miRNA that drastically promotes inflammatory osteoclastogenesis driven by TNF-? and whose expression is suppressed by RBP-J. In our previous project period supported by a K99/R00 grant, we demonstrated and established that RBP-J is a key negative regulator that predominantly restrains TNF-??induced osteoclastogenesis and inflammatory bone resorption. Recently, we found that the RBP-J-regulated miR-182 promotes TNF-? induced osteoclastogenesis via inhibition of Foxo3 and Maml1, two miR-182 direct targets. Thus, suppression of miR-182 by RBP-J may serve as an important mechanism that restrains TNF-? induced osteoclastogenesis. Targeting of the newly described RBP-J-miR-182-Foxo3/Maml1 axis may represent an effective therapeutic approach to suppress inflammatory osteoclastogenesis and bone resorption. In this application, we will apply genetic approaches to further establish the role of the RBP-J-miR- 182-Foxo3/Maml1 axis in vivo and dissect underlying mechanisms. Specifically, we will 1) investigate the role of the RBP-J-miR-182 axis in vivo using genetic approaches; 2) investigate the mechanisms by which miR-182 target, Foxo3, regulates TNF-? induced osteoclastogenesis, and the functional importance of this regulation in vivo. We anticipate that our studies will provide genetic evidence and yield insight into mechanisms that restrain pathologic osteoclastogenesis and inflammatory osteolysis, and will be useful in developing new therapeutic approaches for suppressing bone resorption in inflammatory settings.